1. Field of the Invention
The present invention relates to novel chemical compounds and to the production of nonlinearly optically active organic materials therefrom.
This invention especially relates to high molecular weight organic polymeric materials having a high concentration in recurring structural units that are hyperpolarizable or nonlinearly optically active.
2. Description of the Prior Art
Numerous materials exhibiting nonlinear optical activity are known to this art. Among such materials, the organics typically comprise a polymerizable matrix, in which a hyperpolarizable organic compound is dissolved or incorporated. However, these materials present certain disadvantages, principally by reason of the solubility and compatibility of the organic compound in the matrix.
Furthermore, in such systems, also designated "guest/host" systems, a certain mobility of the hyperpolarizable compounds always remains. Thus, the orientation of the molecules effected by the exposure of the material to an electric field will disappear upon aging, causing a reduction in the nonlinear optical activity thereof.
Polycondensed organic materials containing hyperpolarizable groups grafted onto the principal backbone chain of the polymer via hydrocarbon moieties of varying length, are also known to this art.
As in the aforementioned systems of the "guest/host" type, there remains a certain residual mobility of the hyperpolarizable species, ultimately resulting in a reduction in the nonlinear optical activity upon aging of the material.
Lastly, high molecular weight organic materials are also known to this art, prepared by the polycondensation of a monomer comprising reactive functions borne by a hyperpolarizable group, with a monomer comprising conjugated functions.
Thus, if the reactive functions are hydroxyl radicals, the conjugated monomer may be a diisocyanate.
In such materials, the hyperpolarizable group constitutes a portion of the principal backbone chain or skeleton of the polymer. Consequently, the residual mobility of these groups is significantly reduced, as it requires a mobility of the polymer chain. However, the latter is not zero and it is observed that following the orientation stage under the influence of an electric field, there is a slow return towards disorder, thereby resulting in a gradual loss of the nonlinear (square) optical activity.
For example, published Japanese application No. 88/175,837 describes compounds of this type comprising recurring structural units of the following formulae: ##STR2## wherein L represents a hyperpolarizable group.
It will be appreciated that for a compound to exhibit square nonlinear optical activity, it is also necessary that it be well capable of being oriented under the influence of an electrical field and that it retain this orientation.
Materials exhibiting nonlinear optical activity are generally used in the form of films in optical or optoelectrical devices; these films must be as uniform as possible and have small thicknesses (a few tens of microns, 10.sup.-2 to 10.sup.-1 mm).
The materials described above present the additional major disadvantage of being weakly film-forming and poorly soluble in the solvents typically used to prepare films, such as dichloromethane, dimethylformamide (DMF), N-methylpyrrolidone (NMP), chloroform, cyclohexanone, methylisobutylketone.